67 research outputs found
Role of magnetic fields in fueling Seyfert nuclei
Molecular gas is believed to be the fuel for star formation and nuclear
activity in Seyfert galaxies. To explore the role of magnetic fields in
funneling molecular gas into the nuclear region, measurements of the magnetic
fields embedded in molecular gas are needed. By applying the new velocity
gradient technique (VGT) to ALMA and PAWS's CO isotopolog data, we obtain the
first detection of CO-associated magnetic fields in several nearby Seyfert
galaxies and their unprecedented high-resolution magnetic field maps. The
VGT-measured magnetic fields in molecular gas globally agree with those
inferred from existing HAWC+ dust polarization and VLA synchrotron
polarization. An overall good alignment between the magnetic fields traced by
VGT-CO and by synchrotron polarization may support the correlation between star
formation and cosmic ray generation. We find that the magnetic fields traced by
VGT-CO have a significant radial component in the central regions of most
Seyferts in our sample, where efficient molecular gas inflows or outflows may
happen. In particular, we find local misalignment between the magnetic fields
traced by CO and dust polarization within the nuclear ring of NGC 1097, and the
former aligns with the central bar's orientation. This misalignment reveals
different magnetic field configurations in different gas phases and may provide
an observational diagnostic for the ongoing multi-phase fueling of Seyfert
activity.Comment: 24 pages, 14 figure
Turbulent Magnetic Field Amplification by the Interaction of Shock Wave and Inhomogeneous Medium
Magnetic fields on the order of 100 G observed in young supernova
remnants cannot be amplified by shock compression alone. To investigate the
amplification caused by turbulent dynamo, we perform three-dimensional MHD
simulations of the interaction between shock wave and inhomogeneous density
distribution with a shallow spectrum in the preshock medium. The postshock
turbulence is mainly driven by the strongest preshock density contrast and
cascades to smaller scales. The resulting turbulence amplifies the postshock
magnetic field. The magnetic fields' time evolution agrees with the prediction
of the nonlinear dynamo theory in Xu & Lazarian (2016). When the initial weak
magnetic field is perpendicular to shock normal, the total amplification of the
field's strength achieves a factor of , which is twice larger than
the one in the parallel shock case. However, the strongest magnetic field has a
low volume filling factor and is limited by the turbulent energy due to the
reconnection diffusion taking place in a turbulent and magnetized fluid. The
magnetic field strength averaged along the shock surface is reduced by a factor
. We decompose the turbulent velocity and magnetic field into
solenoidal and compressive modes. The solenoidal mode is dominant and follows
the Kolmogorov scaling, even though the preshock density distribution has a
shallow spectrum. When the preshock density distribution has a Kolmogorov
spectrum, the fraction of the compressive component increases. We find that the
perpendicular shock exhibits a smaller turbulent Alfv\'en Mach number in the
vicinity of the shock front than the parallel shock.Comment: 17 pages, 15 figures, submitted to Ap
Decolourization of remazol brilliant blue R by enzymatic extract and submerged cultures of a newly isolated Pleurotus ostreatus MR3
A local white-rot fungus basidiomycete Pleurotus ostreatus MR3 was isolated from MacRitchie Reservoir Park, Singapore. Among all the ligninolytic activities, laccase was the only enzyme detected in the supernatant when the fungus was grown in liquid culture. This newly isolated white rot fungus was able to completely decolourise remazol brilliant blue R (RBBR) in-vivo on agar plates within five days and in the liquid culture (in the presence of inducers) within three days. The addition of inducers was able to enhance laccase production and therefore enhanced in-vivo RBBR decolourisation. Veratryl alcohol was shown to be the best inducer for laccase production with the maximum laccase activity reaching about 5.99 U/mL. Cu2+ also had a positive effect on laccase production, the laccase activity being enhanced to 5.24 U/mL. In-vitro RBBR decolourisation using the laccase from P. ostreatus MR3 was much comparable to that using the commercial laccase from Trameters versicolor.Keywords: Dyes, remazol brilliant blue R, Pleurotus ostreatus MR3, decolourisation, inducers, laccase activityAfrican Journal of Biotechnology Vol. 12(39), pp. 5778-578
Damping of MHD Turbulence in A Partially Ionized Medium
The coupling state between ions and neutrals in the interstellar medium plays
a key role in the dynamics of magnetohydrodynamic (MHD) turbulence, but is
challenging to study numerically. In this work, we investigate the damping of
MHD turbulence in a partially ionized medium using 3D two-fluid (ions+neutrals)
simulations generated with the AthenaK code. Specifically, we examine the
velocity, density, and magnetic field statistics of the two-fluid MHD
turbulence in different regimes of neutral-ion coupling. Our results
demonstrate that when ions and neutrals are strongly coupled, the velocity
statistics resemble those of single-fluid MHD turbulence. Both the velocity
structures and kinetic energy spectra of ions and neutrals are similar, while
their density structures can be significantly different. With an excess of
small-scale sharp density fluctuations in ions, the density spectrum in ions is
shallower than that of neutrals. When ions and neutrals are weakly coupled, the
turbulence in ions is more severely damped due to the ion-neutral collisional
friction than that in neutrals, resulting in a steep kinetic energy spectrum
and density spectrum in ions compared to the Kolmogorov spectrum. We also find
that the magnetic energy spectrum basically follows the shape of the kinetic
energy spectrum of ions, irrespective of the coupling regime. In addition, we
find large density fluctuations in ions and neutrals and thus spatially
inhomogeneous ionization fractions. As a result, the neutral-ion decoupling and
damping of MHD turbulence take place over a range of length scales.Comment: 17 pages, 14 figures, accepted for publication in MNRA
On the properties and implications of collapse-driven MHD turbulence
We numerically investigate the driving of MHD turbulence by gravitational
contraction using simulations of an initially spherical, magnetically
supercritical cloud core with initially transonic and trans-Alfv\'enic
turbulence. We perform a Helmholtz decomposition of the velocity field, and
investigate the evolution of its solenoidal and compressible parts, as well as
of the velocity component along the gravitational acceleration vector, a proxy
for the infall component of the velocity field. We find that: 1) In spite of
being supercritical, the core first contracts to a sheet perpendicular to the
mean field, and the sheet itself collapses. 2) The solenoidal component of the
turbulence remains at roughly its initial level throughout the simulation,
while the compressible component increases continuously. This implies that
turbulence does {\it not} dissipate towards the center of the core. 3) The
distribution of simulation cells in the - plane occupies a wide
triangular region at low densities, bounded below by the expected trend for
fast MHD waves (, applicable for high local Alfv\'enic Mach
number \Ma) and above by the trend expected for slow waves (
constant, applicable for low local \Ma). At high densities, the distribution
follows a single trend B \propto \rho^{\gamef}, with 1/2 < \gamef < 2/3, as
expected for gravitational compression. 4) The measured mass-to-magnetic flux
ratio increases with radius , due to the different scalings of the
mass and magnetic flux with . At a fixed radius, increases with
time due to the accretion of material along field lines. 5) The solenoidal
energy fraction is much smaller than the total turbulent component, indicating
that the collapse drives the turbulence mainly compressibly, even in directions
orthogonal to that of the collapse.Comment: Resubmitted to MNRAS after first set of reviewer's recommendations.
Comments welcom
Analysis of Effect of Schisandra in the Treatment of Myocardial Infarction Based on Three-Mode Gene Ontology Network
Schisandra chinensis is a commonly used traditional Chinese medicine, which has been widely used in the treatment of acute myocardial infarction in China. However, it has been difficult to systematically clarify the major pharmacological effect of Schisandra, due to its multi-component complex mechanism. In order to solve this problem, a comprehensive network analysis method was established based-on âcomponentâgene ontologyâeffectâ interactions. Through the network analysis, reduction of cardiac preload and myocardial contractility was shown to be the major effect of Schisandra components, which was further experimentally validated. In addition, the expression of NCOR2 and NFAT in myocyte were experimentally confirmed to be associated with Schisandra in the treatment of AMI, which may be responsible for the preservation effect of myocardial contractility. In conclusion, the three-mode gene ontology network can be an effective network analysis workflow to evaluate the pharmacological effects of a multi-drug complex system
Cosmic ray propagation in turbulent magnetic fields
Propagation of cosmic rays (CRs) in turbulent and magnetized astrophysical media is a long-standing problem that requires both understanding of the properties of turbulent magnetic fields and their interaction with energetic particles. This review focuses on selected recent theoretical findings made based on the progress in understanding and simulating magnetohydrodynamic (MHD) turbulence. In particular, we address the problem of perpendicular and parallel propagation of CRs and identify the conditions when the perpendicular propagation is superdiffusive and diffusive. For the parallel diffusion, we discuss the problems of the traditionally used diffusion mechanism arising from pitch angle scattering and the possible solutions provided by the recently identified âmirror diffusionâ in the presence of turbulent magnetic mirrors
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