51 research outputs found
Frame-dragging effects on magnetic fields near a rotating black hole
We discuss the role of general relativity frame dragging acting on magnetic
field lines near a rotating (Kerr) black hole. Near ergosphere the magnetic
structure becomes strongly influenced and magnetic null points can develop. We
consider aligned magnetic fields as well as fields inclined with respect to the
rotation axis, and the two cases are shown to behave in profoundly different
ways. Further, we construct surfaces of equal values of local electric and
magnetic intensities, which have not yet been discussed in the full generality
of a boosted rotating black hole.Comment: to appear in the proceedings of "The Central Kiloparsec in Galactic
Nuclei (AHAR 2011)", Journal of Physics: Conference Series (JPCS), IOP
Publishin
Regular and Chaotic Motion in General Relativity: The Case of a Massive Magnetic Dipole
Circular motion of particles, dust grains and fluids in the vicinity of
compact objects has been investigated as a model for accretion of gaseous and
dusty environment. Here we further discuss, within the framework of general
relativity, figures of equilibrium of matter under the influence of combined
gravitational and large-scale magnetic fields, assuming that the accreted
material acquires a small electric charge due to interplay of plasma processes
and photoionization. In particular, we employ an exact solution describing the
massive magnetic dipole and we identify the regions of stable motion. We also
investigate situations when the particle dynamics exhibits the onset of chaos.
In order to characterize the measure of chaoticness we employ techniques of
Poincar\'e surfaces of section and of recurrence plots.Comment: 11 pages, 6 figures, published in the proceedings of the conference
"Relativity and Gravitation: 100 Years after Einstein in Prague" (25. - 29.
6. 2012, Prague
Transition from Regular to Chaotic Circulation in Magnetized Coronae near Compact Objects
Accretion onto black holes and compact stars brings material in a zone of
strong gravitational and electromagnetic fields. We study dynamical properties
of motion of electrically charged particles forming a highly diluted medium (a
corona) in the regime of strong gravity and large-scale (ordered) magnetic
field. We start our work from a system that allows regular motion, then we
focus on the onset of chaos. To this end, we investigate the case of a rotating
black hole immersed in a weak, asymptotically uniform magnetic field. We also
consider a magnetic star, approximated by the Schwarzschild metric and a test
magnetic field of a rotating dipole. These are two model examples of systems
permitting energetically bound, off-equatorial motion of matter confined to the
halo lobes that encircle the central body. Our approach allows us to address
the question of whether the spin parameter of the black hole plays any major
role in determining the degree of the chaoticness. To characterize the motion,
we construct the Recurrence Plots (RP) and we compare them with Poincar\'e
surfaces of section. We describe the Recurrence Plots in terms of the
Recurrence Quantification Analysis (RQA), which allows us to identify the
transition between different dynamical regimes. We demonstrate that this new
technique is able to detect the chaos onset very efficiently, and to provide
its quantitative measure. The chaos typically occurs when the conserved energy
is raised to a sufficiently high level that allows the particles to traverse
the equatorial plane. We find that the role of the black-hole spin in setting
the chaos is more complicated than initially thought.Comment: 21 pages, 20 figures, accepted to Ap
Magnetic layers and neutral points near rotating black hole
Magnetic layers are narrow regions where the field direction changes sharply.
They often occur in the association with neutral points of the magnetic field.
We show that an organised field can produce these structures near a rotating
black hole, and we identify them as potential sites of magnetic reconnection.
To that end we study the field lines affected by the frame-dragging effect,
twisting the magnetic structure and changing the position of neutral points. We
consider oblique fields in vacuum. We also include the possibility of
translational motion of the black hole which may be relevant when the black
hole is ejected from the system. The model settings apply to the innermost
regions around black holes with the ergosphere dominated by a
super-equipartition magnetic field and loaded with a negligible gas content.Comment: 10 pages, 3 figures, Classical and Quantum Gravity accepte
anti-tick vaccines to prevent tick-borne diseases in Europe
Ixodes ricinus transmits bacterial, protozoal and viral pathogens, causing
disease and forming an increasing health concern in Europe. ANTIDotE is an
European Commission funded consortium of seven institutes, which aims to
identify and characterize tick proteins involved in feeding and pathogen
transmission. The knowledge gained will be used to develop and evaluate anti-
tick vaccines that may prevent multiple human tick-borne diseases. Strategies
encompassing anti-tick vaccines to prevent transmission of pathogens to
humans, animals or wildlife will be developed with relevant stakeholders with
the ultimate aim of reducing the incidence of tick-borne diseases in humans
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Northern Eurasia Future Initiative (NEFI): facing the challenges and pathways of global change in the 21st century
During the past several decades, the Earth system has changed significantly, especially across Northern Eurasia. Changes in the socio-economic conditions of the larger countries in the region have also resulted in a variety of regional environmental changes that can
have global consequences. The Northern Eurasia Future Initiative (NEFI) has been designed as an essential continuation of the Northern Eurasia Earth Science
Partnership Initiative (NEESPI), which was launched in 2004. NEESPI sought to elucidate all aspects of ongoing environmental change, to inform societies and, thus, to
better prepare societies for future developments. A key principle of NEFI is that these developments must now be secured through science-based strategies co-designed
with regional decision makers to lead their societies to prosperity in the face of environmental and institutional challenges. NEESPI scientific research, data, and
models have created a solid knowledge base to support the NEFI program. This paper presents the NEFI research vision consensus based on that knowledge. It provides the reader with samples of recent accomplishments in regional studies and formulates new NEFI science questions. To address these questions, nine research foci are identified and their selections are briefly justified. These foci include: warming of the Arctic; changing frequency, pattern, and intensity of extreme and inclement environmental conditions; retreat of the cryosphere; changes in terrestrial water cycles; changes in the biosphere; pressures on land-use; changes in infrastructure; societal actions in response to environmental change; and quantification of Northern Eurasia's role in the global Earth system. Powerful feedbacks between the Earth and human systems in Northern Eurasia (e.g., mega-fires, droughts, depletion of the cryosphere essential for water supply, retreat of sea ice) result from past and current human activities (e.g., large scale water withdrawals, land use and governance change) and
potentially restrict or provide new opportunities for future human activities. Therefore, we propose that Integrated Assessment Models are needed as the final stage of global
change assessment. The overarching goal of this NEFI modeling effort will enable evaluation of economic decisions in response to changing environmental conditions and justification of mitigation and adaptation efforts
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