42 research outputs found
FSRQ/BL Lac dichotomy as the magnetized advective accretion process around black holes: a unified classification of blazars
The blazar observations show a strong correlation between
-ray luminosities and spectral indices. BL Lac objects are less
luminous with harder spectra than flat-spectrum radio quasars (FSRQs).
Interestingly FSRQs are evident to exhibit a Keplerian disc component along
with a powerful jet. We compute the jet intrinsic luminosities by beaming
corrections determined by different cooling mechanisms. Observed -ray
luminosities and spectroscopic measurements of broad emission lines suggest a
correlation of the accretion disc luminosity with jet intrinsic luminosity.
Also, theoretical and observational inferences for these jetted sources
indicate a signature of hot advective accretion flow and a dynamically dominant
magnetic field at jet-footprint. Indeed it is difficult to imagine the powerful
jet launching from a geometrically thin Keplerian disc. We propose a
magnetized, advective disc-outflow symbiosis with explicit cooling to address a
unified classification of blazars by controlling both the mass accretion rate
and magnetic field strength. The large scale strong magnetic fields influence
the accretion dynamics, remove angular momentum from the infalling matter, help
in the formation of strong outflows/jets, and lead to synchrotron emissions
simultaneously. We suggest that the BL Lacs are more optically thin and
magnetically dominated than FSRQs at the jet-footprint to explain their
intrinsic -ray luminosities.Comment: 8 pages including 4 figures; Accepted for publication in MNRA
Magnetized advective accretion flows: formation of magnetic barriers in Magnetically Arrested Discs
We discuss the importance of large scale strong magnetic field in the removal
of angular momentum outward, as well as the possible origin of different kinds
of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion
flows around black holes. The origin of this large scale strong magnetic field
near the event horizon is due to the advection of the magnetic flux by the
accreting gas from the environment, say, the interstellar medium or a companion
star, because of flux freezing. In this simplest vertically averaged,
1.5-dimensional disc model, we choose the maximum upper limit of the magnetic
field, which the disc around a black hole can sustain. In this so called
magnetically arrested disc (MAD) model, the accreting gas either decelerates or
faces the magnetic barrier near the event horizon by the accumulated magnetic
field depending on the geometry. The magnetic barrier may knock the matter to
infinity. We suggest that these types of flow are the building block to produce
jets and outflows in the accreting system. We also find that in some cases,
when matter is trying to go back to infinity after knocking the barrier, matter
is prevented being escaped by the cumulative action of strong gravity and the
magnetic tension, hence by another barrier. In this way, magnetic field can
lock the matter in between these two barriers and it might be a possible
explanation for the formation of episodic jet.Comment: 16 pages including 15 figures; Accepted for publication in MNRA
A unified treatment of mean-field dynamo and angular-momentum transport in magnetorotational instability-driven turbulence
Magnetorotational instability (MRI)-driven turbulence and dynamo phenomena
are analyzed using direct statistical simulations. Our approach begins by
developing a unified mean-field model that combines the traditionally decoupled
problems of the large-scale dynamo and angular-momentum transport in accretion
disks. The model consists of a hierarchical set of equations, capturing up to
the second-order cumulants, while a statistical closure approximation is
employed to model the three-point correlators. We highlight the web of
interactions that connect different components of stress tensors -- Maxwell,
Reynolds, and Faraday -- through shear, rotation, correlators associated with
mean fields, and nonlinear terms. We determine the dominant interactions
crucial for the development and sustenance of MRI turbulence. Our general mean
field model for the MRI-driven system allows for a self-consistent construction
of the electromotive force, inclusive of inhomogeneities and anisotropies.
Within the realm of large-scale magnetic field dynamo, we identify two key
mechanisms -- the rotation-shear-current effect and the
rotation-shear-vorticity effect -- that are responsible for generating the
radial and vertical magnetic fields, respectively. We provide the explicit
(nonperturbative) form of the transport coefficients associated with each of
these dynamo effects. Notably, both of these mechanisms rely on the intrinsic
presence of large-scale vorticity dynamo within MRI turbulence.Comment: 32 pages, 25 figures; Comments welcom
Quantum Effects on Dynamic Structure Factors in Dense Magnetized Plasmas
We extend the classical magnetohydrodynamics formalism to include nonlocal
quantum behavior via the phenomenological Bohm potential. We then solve the
quantum magnetohydrodynamics equations to obtain a new analytical form of the
dynamic structure factor (DSF), a fundamental quantity linking theory and
experiments. Our results show that the three-peak structure -- one central
Rayleigh peak and two Brillouin peaks -- of the DSF arising from quantum
hydrodynamic fluctuations becomes (in general) a five-peak structure -- one
central Rayleigh peak and two pairs of peaks associated with fast and slow
magnetosonic waves. The Bohm contribution influences the positions and
characteristics (height, width, and intensity) of the peaks by introducing
three significant modifications: (a) an increase in effective thermal pressure,
(b) a reduction in the adiabatic index, and (c) an enhancement of effective
thermal diffusivity. The multiple DSF peaks enable concurrent measurements of
diverse plasma properties, transport coefficients, and thermodynamic parameters
in magnetized dense plasmas. The potential for experimental validation of our
theory looms large, particularly through future experiments conducted at
state-of-the-art laser facilities.Comment: 13 pages including 5 figures and 1 table; Comments are welcom
Impacts of biomedical hashtag-based Twitter campaign: #DHPSP utilization for promotion of open innovation in digital health, patient safety, and personalized medicine
The open innovation hub Digital Health and Patient Safety Platform (DHPSP) was recently established with the purpose to invigorate collaborative scientific research and the development of new digital products and personalized solutions aiming to improve human health and patient safety. In this study, we evaluated the effectiveness of a Twitter-based campaign centered on using the hashtag #DHPSP to promote the visibility of the DHPSP initiative. Thus, tweets containing #DHPSP were monitored for five weeks for the period 20.10.2020–24.11.2020 and were analyzed with Symplur Signals (social media analytics tool). In the study period, a total of 11,005 tweets containing #DHPSP were posted by 3020 Twitter users, generating 151,984,378 impressions. Analysis of the healthcare stakeholder-identity of the Twitter users who used #DHPSP revealed that the most of participating user accounts belonged to individuals or doctors, with the top three user locations being the United States (501 users), the United Kingdom (155 users), and India (121 users). Analysis of co-occurring hashtags and the full text of the posted tweets further revealed that the major themes of attention in the #DHPSP Twitter-community were related to the coronavirus disease 2019 (COVID-19), medicine and health, digital health technologies, and science communication in general. Overall, these results indicate that the #DHPSP initiative achieved high visibility and engaged a large body of Twitter users interested in the DHPSP focus area. Moreover, the conducted campaign resulted in an increase of DHPSP member enrollments and website visitors, and new scientific collaborations were formed. Thus, Twitter campaigns centered on a dedicated hashtag prove to be a highly efficient tool for visibility-promotion, which could be successfully utilized by healthcare-related open innovation platforms or initiatives