163 research outputs found
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
The modification of the Vlasov equation, in its standard form describing a
charged particle distribution in the six-dimensional phase space, is derived
explicitly within a formal Hamiltonian approach for arbitrarily curved
spacetime. The equation accounts simultaneously for the Lorentz force and the
effects of general relativity, with the latter appearing as the gravity force
and an additional force due to the extrinsic curvature of spatial
hypersurfaces. For an arbitrary spatial metric, the equations of collisionless
hydrodynamics are also obtained in the usual three-vector form
Nonlinear dispersion of stationary waves in collisionless plasmas
A nonlinear dispersion of a general stationary wave in collisionless plasma
is obtained in a non-differential form from a single-particle
oscillation-center Hamiltonian. For electrostatic oscillations in nonmagnetized
plasma, considered as a paradigmatic example, the linear dielectric function is
generalized, and the trapped particle contribution to the wave frequency shift
is found analytically as a function of the wave amplitude .
Smooth distributions yield , as usual. However,
beam-like distributions of trapped electrons result in different power laws, or
even a logarithmic nonlinearity, which are derived as asymptotic limits of the
same dispersion relation
Adiabatic nonlinear waves with trapped particles: II. Wave dispersion
A general nonlinear dispersion relation is derived in a nondifferential form
for an adiabatic sinusoidal Langmuir wave in collisionless plasma, allowing for
an arbitrary distribution of trapped electrons. The linear dielectric function
is generalized, and the nonlinear kinetic frequency shift is
found analytically as a function of the wave amplitude . Smooth
distributions yield , as usual. However,
beam-like distributions of trapped electrons result in different power laws, or
even a logarithmic nonlinearity, which are derived as asymptotic limits of the
same dispersion relation. Such beams are formed whenever the phase velocity
changes, because the trapped distribution is in autoresonance and thus evolves
differently from the passing distribution. Hence, even adiabatic is generally nonlocal.Comment: submitted together with Papers I and II
Penetration of a radio frequency electromagnetic field into a magnetized plasma: one-dimensional PIC simulation studies
Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma
Equations describing the linear evolution of a non-dissipative Langmuir wave
in inhomogeneous nonstationary anisotropic plasma without magnetic field are
derived in the geometrical optics approximation. A continuity equation is
obtained for the wave action density, and the conditions for the action
conservation are formulated. In homogeneous plasma, the wave field E
universally scales with the electron density N as E ~ N^{3/4}, whereas the
wavevector evolution varies depending on the wave geometry
A 'Rosetta Stone' for protoplanetary disks:the synergy of multi-wavelength observations
The recent progress in instrumentation and telescope development has brought
us different ways to observe protoplanetary disks, including interferometers,
space missions, adaptive optics, polarimetry, and time- and spectrally-resolved
data. While the new facilities have changed the way we can tackle the existing
open problems in disk structure and evolution, there is a substantial lack of
interconnection between different observing techniques and their user
communities. Here, we explore the complementarity of some of the
state-of-the-art observing techniques, and how they can be brought together in
a collective effort to understand how disks evolve and disperse at the time of
planet formation.
This paper was born at the "Protoplanetary Discussions" meeting in Edinburgh,
2016. Its goal is to clarify where multi-wavelength observations of disks
converge in unveiling disk structure and evolution, and where they diverge and
challenge our current understanding. We discuss caveats that should be
considered when linking results from different observations, or when drawing
conclusions based on limited datasets (in terms of wavelength or sample). We
focus on disk properties that are currently being revolutionized by
multi-wavelength observations. Specifically: the inner disk radius, holes and
gaps and their link to large-scale disk structures, the disk mass, and the
accretion rate. We discuss how the links between them, as well as the apparent
contradictions, can help us to disentangle the disk physics and to learn about
disk evolution.Comment: Accepted for publication in PASA. 37 pages, 9 figures, 1 table.
Revised version: corrected problem in Fig
Long-term multiwavelength monitoring and reverberation mapping of NGC 2617 during a changing-look event
We present the results of photometric and spectroscopic monitoring campaigns
of the changing look AGN NGC~2617 carried out from 2016 until 2022 and covering
the wavelength range from the X-ray to the near-IR. The facilities included the
telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope,
Swift, and others. We found significant variability at all wavelengths and,
specifically, in the intensities and profiles of the broad Balmer lines. We
measured time delays of ~ 6 days (~ 8 days) in the responses of the H-beta
(H-alpha) line to continuum variations. We found the X-ray variations to
correlate well with the UV and optical (with a small time delay of a few days
for longer wavelengths). The K-band lagged the B band by 14 +- 4 days during
the last 3 seasons, which is significantly shorter than the delays reported
previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises
from two different emission regions: the outer part of the accretion disc and a
more distant dust component. The HK-band variability is governed primarily by
dust. The Balmer decrement of the broad-line components is inversely correlated
with the UV flux. The change of the object's type, from Sy1 to Sy1.8, was
recorded over a period of ~ 8 years. We interpret these changes as a
combination of two factors: changes in the accretion rate and dust recovery
along the line of sight.Comment: 14 pages, 15 figures, accepted by the MNRA
Storing, Retrieving, and Processing Optical Information by Raman Backscattering in Plasmas
Flaxseed supplementation improved insulin resistance in obese glucose intolerant people: a randomized crossover design
<p>Abstract</p> <p>Background</p> <p>Obesity leads to an increase in inflammation and insulin resistance. This study determined antioxidant activity of flaxseed and its role in inflammation and insulin resistance in obese glucose intolerant people.</p> <p>Methods</p> <p>Using a randomized crossover design, nine obese glucose intolerant people consumed 40 g ground flaxseed or 40 g wheat bran daily for 12 weeks with a 4-week washout period. Plasma inflammation biomarkers (CRP, TNF-α, and IL-6), glucose, insulin, and thiobaribituric acid reactive substance (TBARS) were measured before and after of each supplementation.</p> <p>Results</p> <p>Flaxseed supplementation decreased TBARS (p = 0.0215) and HOMA-IR (p = 0.0382). Flaxseed or wheat bran supplementation did not change plasma inflammatory biomarkers. A positive relationship was found between TBARS and HOMA-IR (r = 0.62, p = 0.0003).</p> <p>Conclusions</p> <p>The results of the study weakly support that decreased insulin resistance might have been secondary to antioxidant activity of flaxseed. However, the mechanism(s) of decreased insulin resistance by flaxseed should be further determined using flaxseed lignan.</p
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